Several mining methods have recently been tried aspossible ways of overcoming a variety of geotechnical problemsencountered during underground extraction of thick coal seams inthe different conditions of some of India's coalfields and soincreasing production, productivity and safety. Strata—controlobservations were recorded during extraction by mechanizedlongwall sub-level caving, wide-stall mining, mechanizeddepillaring based on cable-bolting, sub-level caving with artificialroofing and hydraulic mining. The strengths and weaknesses ofthese methods are discussed in the context of the geotechnical problems.Field monitoring revealed excessive load on chock shieldsupport during the mechanized longwall sublevel caving of a thickseam. Laboratory simulation of the mining conditions in thecoalfield indicated that the impact of an indirect increase ofextraction height and the load of broken roof strata attributable totop-section working had to be considered in the design of supportfor such workings.By taking advantage of competent roof strata, an adequate depthof cover and the rapid increase of pillar strength with increase inits size the splitting and stooking method that has been used tooptimize the recovery of coal from a seam developed undersurface structures in a built-up area is being replaced by wideningof existing galleries. This method of partial extraction, called'wide-stall mining', provides better safety and recovery than theconventional method.In another investigation these massiveness of the coal seamplayed an important role during the application of cable-bolting toprovide effective support to the high roof as well as the overlyingcoal bed. Encouraging results were obtained in a field trial ofdepillaring the complete thickness of a developed thick seam inone lift with the aid of full-column grouted steel cable.
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